Lecture by Justin London: Where is the beat in that note?

When coordinating physical actions with sounds, we synchronise our actions with the perceptual center (P-center) of the sound, understood as the specific moment at which the sound is perceived to occur. Using matched sets of real and artificial musical sounds as stimuli, we probed the influence of Attack (rise time), Duration, and Frequency (spectral centroid) on perceived P-center location and P-center variability. Two different methods to determine the P-centers were used: Clicks aligned in-phase with the target sounds via the method of adjustment, and tapping in synchrony with the target sounds. We found that attack and duration are primary cues for P-center location and P-center variability, and that the latter is a useful measure of P-center shape. Probability density distributions for each stimulus display a systematic pattern of P-center shapes ranging from narrow peaks close to the onset of sounds with a fast attack and short duration, to wider and flatter shapes indicating a range synchronization points for sounds with a slow attack and long duration. The results show that P-centers are not simply time points, but "beat bins" with characteristic shapes, and the shapes and locations of these beat bins are dependent upon both the stimulus and the synchronization task.